This invention relates in general to machine tools and finishing operations for vehicle wheels and in particular to machine tools and finishing operations for vehicle wheels that reduce radial runout.
One conventional process for manufacturing vehicle wheels involves pouring molten metal into a wheel mold to form a one piece wheel casting. Typically, one piece wheels are cast with an alloy of a light metal, such as aluminum. After the molten metal solidifies, the wheel casting is removed from the mold. The wheel casting is oversized and is machined to final shape.
Another process involves, a full face wheel disc, which includes the outboard tire bead retaining flange, that is cast or forged from a lightweight alloy and-machined to final shape. A partial wheel rim, which can be rolled from a strip of metal, for example steel, is then welded to an inboard surface of the wheel disc to form a two piece wheel. Such a wheel can combine the low cost and strength of a steel rim with a pleasing aesthetic appearance of a wheel disc cast from a lightweight metal and is usually referred to as a bimetal wheel.
A third process utilizes a wheel disc stamped from steel that is welded to a rolled full wheel rim to form a wheel.
Machining a wheel or wheel disc, regardless of how formed, typically includes multiple operations. First, sawing machines cut casting gates and risers from wheel castings. Then, a drilling machine is used to drill wheel mounting holes through the wheel hub. Next, the wheel is mounted upon a wheel lathe for machining to its final shape. During the lathe operations, the wheel is rotated and a cutting tool is applied against the wheel surfaces. The inside surface of the wheel hub is usually faced to provide a flat mounting surface. Similarly, the outboard wheel disc surface is finished to its final contour. Then, the outside of the wheel rim is turned to its final shape. Optionally, the inside surface of the wheel rim may also be turned to a final shape. The inboard and outboard tire beadseats are turned. The central pilot hole is usually drilled while the casting is clamped in the lathe for turning the inboard tire beadseat.
Referring to the drawings, FIG. 1 illustrates a typical one piece vehicle wheel 10. The vehicle wheel 10 can be cast or forged from an aluminum alloy to produce a wheel casting or forging having physical dimensions that are close to the desired final wheel dimensions. The casting is then machined to the desired final dimensions. Vehicle wheels also may be formed from any other suitable material, such as steel, and may be formed by any other suitable process, such as welding a partial wheel rim rolled from a strip of steel to a cast full face wheel disc.
The vehicle wheel 10 includes an annular wheel rim 20, which carries a tire. The annular wheel rim 20 of the vehicle wheel 10 has an inner annular surface 22 and an outer annular surface 24. An inboard tire beadseat 26 and an outboard tire beadseat 28, which support the tire beads formed upon the ends of the walls of a pneumatic tire (not shown), are formed on the outer annular surface 24 at the inboard and outboard ends 27 and 29 of the wheel rim 20. The inboard and outboard tire beadseats 27 and 29 cooperate with the tire beads of the pneumatic tire (not shown) to form a seal. In addition, wheel flanges 30 and 31 and safety humps 32 and 33 are formed at the inboard and outboard ends 27 and 29 of the rim 20 for retaining the pneumatic tire (not shown) on the vehicle wheel 10.
The vehicle wheel 10 also includes a circular inner wheel disc 12 formed across the outboard end 29 of the annular wheel rim 20. The inner wheel disc 12 has a central hub portion 14 supported within the annular wheel rim 20 by a plurality of wheel spokes 19. The inner wheel disc 12 mounts the vehicle wheel 10 on an associated drive member (not shown), such as a vehicle axle. The central hub portion 14 has a central pilot hole 16 cast and machined therein, in which the associated drive member end is closely received. A plurality of wheel bolt holes 18 are cast into the central hub portion 14 for receiving wheel studs, which cooperate with wheel nuts, to secure the vehicle wheel to the associated drive member. Alternatively, the central pilot hole 16 and the plurality of wheel bolt holes 18 may be machined into the central hub portion 14 using conventional machining techniques.
When the vehicle wheel 10 is machined, the inboard and outboard tire beadseats 26 and 28 are turned. To minimize vibration, it is desirable that the inboard and outboard tire beadseats 26 and 28 have uniform radii, meaning that every point on the beadseats 26 and 28 be equidistant from a central axis Z of the vehicle wheel 10. Ideally, the beadseats 26 and 28 are perfect circles with centers that are coincident with the central axis Z of the vehicle wheel 10. A measure of the tire beadseat radial uniformity is radial runout. Radial runout is the radial distance between the xe2x80x9chighest pointxe2x80x9d and the xe2x80x9clowest pointxe2x80x9d on the annular wheel rim 20 as measured from the axis Z of the vehicle wheel 10. As shown in FIG. 1, the radial runout of the outboard tire bead seat 28 can be described as the difference between two radii X and Y, where X is the shortest radial distance from the axis Z to the outboard tire beadseat 28 and Y is the longest radial distance from the axis Z to the outboard tire beadseat 28.
This invention relates in general to machine tools and finishing operations for vehicle wheels and in particular to machine tools and finishing operations for vehicle wheels that reduce radial runout.
When the outside surface of the wheel rim is machined, the tire beadseats are turned. Even when machined under optimal conditions a vehicle wheel rim will have some radial runout. Machining upon a conventional wheel lathe, the current processes for finishing the beadseats, is, at best, typically capable of producing a radial runout within a range of 0.005 inches (0.127 Millimeters) to 0.010 inches (0.258 Millimeters). Radial runout will tend to increase when machining conditions are less than optimal, for example, when the wheel is not mounted upon the lathe with the wheel axis coincident with the lathe axis. Excessive radial runout in the tire beadseats may cause undesirable vibrations in a vehicle even when the tires and wheels have been balanced. Accordingly, it would be desirable to reduce radial runout.
The present invention contemplates using an Electric Discharge Machining (EDM) apparatus for machining tire beadseats to reduce radial runout. EDM is a thermal erosion process in which material is removed by a series of recurring electrical discharges between an electrode and a workpiece, in the presence of a dielectric fluid. The EDM apparatus includes a support structure that is adapted to support a vehicle wheel. The apparatus further includes an electrode for machining at least one beadseat of the vehicle wheel.
The invention also contemplates a method for using the apparatus that includes the step of providing an EDM apparatus having at least one electrode. A vehicle wheel is mounted upon the EDM apparatus. The vehicle wheel is immersed in a dielectric fluidic bath and then rotated. The vehicle wheel is then moved toward the electrode and voltage is applied to the electrode. As the vehicle wheel continues to move toward the electrode, at least one spark is generated between the electrode and the vehicle wheel. The resulting spark removes material from the tire beadseats of the vehicle wheel to reduce radial runout.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.